Running OpenLDAP 2.3.4 as a 64 bit build on an AMD opteron, I could
core dump slapd repeatedly using SASL/GSSAPI binds. This problem only
occurs on 64 bit builds (32 bit builds run for hours with no issues),
and appeared to be coming from Heimdal, rather than OpenLDAP (I was
using heimdal-0.7). I put it under valgrind-3.0 (you can check this
out from their subversion respository), and tried to get leak data out
of slapd, but was unable to find anything other than the bits you've
noted as well. The heimdal folks did give me two patches for leaks
they found in a 32 bit environment, but neither of those patches
solved the problem. So at this point, it is not clear where
specifically the problem lies (somewhere between slapd & heimdal).

For 64 bit builds you might try my current FunctionCheck (1.5.4)
instead, for leak tracing. valgrind 3.0 is still very limited on AMD64,
and its memory layout makes using it on large databases pretty much
impossible.